1. Field of the Invention
The present invention relates generally to lamp modules, and more particularly to an electronic module for dimming a lighting fixture near a minimum current capability of a lighting fixture driver.
2. Description of the Background of the Invention
Lamp drivers have been devised that provide power to one or more lamp loads, such as one or more light emitting diodes (LEDs). Using LEDs in lamps has become particularly popular of late because LEDs develop a very bright light output while consuming relatively little power compared to other types of lamps.
Some lamp drivers have been designed to provide variable power to LEDs to obtain a dimming effect. Such drivers may provide variable power in response to a user input or according to a predetermined schedule that is implemented by a controller. In known designs for driving one or more LEDs in a dimmable manner, the lamp driver receives power from a power supply (such as residential or commercial power supplied by an electric utility) to power circuit element(s) that develop a driving current.
In order to dim an LED, drivers typically reduce the average current delivered to the LEDs. Specifically, an alternating current (AC) waveform is typically phase controlled in accordance with a dimming control signal to control average current. Less average current typically translates into less light intensity. However, such a control scheme can be problematic when attempting to dim an LED lamp to very low levels of light intensity. AC/DC power supplies typically suffer from a minimum load requirement which start to affect performance at approximately 1/10th to 1/20th rated power output. Power supplies typically go into burst mode under these light load conditions to maintain a constant output. Thus, any power level requested below these limits can cause instability in the light levels and produce side effects such as blinking, flicker, audible noise, or even complete loss of light.